A more informative approach for characterization of polymer monolithic phases: small angle neutron scattering/ultrasmall angle neutron scattering

Neutron scattering techniques have been used frequently to characterize geological specimens and to determine the structures of glasses and of polymers as solutions, suspensions, or melts. Little work has been reported on their application in determining polymers' structural properties relevant to separations. Here, we present a comparison of characterization results from nitrogen porosimetry and from combined small angle neutron scattering (SANS) and ultrasmall angle neutron scattering (USANS) experiments. We show that SANS is extremely sensitive to the pore characteristics. Both approaches can provide information about porosity and pore characteristics, but the neutron scattering techniques provide additional information in the form of the surface characteristics of the pores and their length scales. Fits of the scattering data show that cylindrical pores are present with diameters down to 0.6 μm and that, for length scales down to approxmately 20 ?, the material shows self-similar (fractal) slopes of -3.4 to -3.6. Comparison of these characteristics with other examples from the scattering literature indicate that further investigation of their meaning for chromatographic media is required.     

Porous ceramic bone scaffolds for vascularized bone tissue regeneration

Hydroxyapatite scaffolds with a multi modal porosity designed for use in tissue engineering of vascularized bone graft substitutes were prepared by three dimensional printing. Depending on the ratio of coarse (mean particle size 50 microm) to fine powder (mean particle size 4 microm) in the powder granulate and the sintering temperature total porosity was varied from 30% to 64%. While macroscopic pore channels with a diameter of 1 mm were created by CAD design, porosity structure in the sintered solid phase was governed by the granulate structure of the printing powder. Scaffolds sintered at 1,250 degrees C were characterized by a bimodal pore structure with intragranular pores of 0.3-0.4 microm and intergranular pores of 20 microm whereas scaffolds sintered at 1,400 degrees C exhibit a monomodal porosity with a maximum of pore size distribution at 10-20 microm. For in-vivo testing, matrices were implanted subcutaneously in four male Lewis rats. Scaffolds with 50% porosity and an average pore size of approximately 18 microm were successfully transferred to rats and vascularized within 4 weeks.     

Effect of submicron grains on ionic conductivity of nanocrystalline doped ceria

Doped ceria has been considered for high oxygen ion conductivity for solid oxide fuel cells. In the present study, 20 mole% samarium doped nano ceria powder was prepared by wet chemical synthesis and sintered at different temperatures to retain submicron grains (> 92-96% density). ionic conductivity of the sintered pellets was measured using impedance spectroscopy as a function of temperature (200-800 degrees C). The total maximum conductivity was 1.0 x 10(-2)S.cm(-1) (at 600 degrees C) for samples sintered at 1200 degrees C. The activation energy at higher test temperature decreases with the decrease in the sintering temperature (by 25%). The grain boundary, grain interior conductivity and activation energy of the electrolyte were correlated to the resulting microstructure. It has been demonstrated that use of doped nano ceria powder as precursor not only reduced the sintering temperature but also provided segregation free grain boundary for engineering higher conductivity dense electrolytes.     

Synthesis of yttria-doped bismuth oxide powder by carbonate coprecipitation for IT-SOFC electrolyte

Yttria-doped bismuth oxide (YBO) powders were synthesized by ammonium carbonate coprecipitation for the preparation of electrolytes of an intermediate temperature solid oxide fuel cell (IT-SOFC). The starting salts were yttrium and bismuth nitrate. The crystal structures and the morphological characteristics of the particles were analyzed by XRD and SEM, respectively. The ionic conductivity of the sintered pellet was measured by an electrochemical impedance analyzer. The size of the calcined YBO powders were in the range of 20-100 nm as measured by SEM images. The YBO pellets had a face-centered cubic structure, and their crystallite size was about 54-88 nm. The ionic conductivity of the YBO pellets sintered at 800 degrees C was observed to be 2.7 x 10(-1) Scm-(-1) at 700 degrees C. The ball-milling of the YBO powder before it was pelletized was found to have been unrequired probably because of a good sinterability of the YBO powders that was prepared via the ammonium carbonate coprecipitation method. The results showed that the ammonium carbonate coprecipitation process could be used as the cost-efficient method of producing YBO electrolytes for IT-SOFC.     

Permeation of solvents through disk type rice husk silica membrane modified with alkyl silylation reagents

Rice husk silica (RHS) which was obtained with thermal treatment of rice husk has the size of approximately 10 micrometer with 4-5 nm pore. RHS can be mold to a disk type membrane. The membrane may have submicron pore originated from the space among the particles, and the nano pores of the rice husk silica (RHS pore). Even it is difficult to adjust the size of the pores, we can suggest that the membrane shows different permeability for the organic/inorganic solvents if the affinity between the surface of the pores and the permeating molecule is changed. In this study, we investigated the permeation of the typical solvents such as water, ethanol and toluene to the RHS membranes sintered at 1100 degrees C, 1150 degrees C and 1200 degrees C and modified with triethoxymethyl silane (CH3)Si(C2H5O)3, diethoxydiemethyl silane (CH3)2Si(C2H5O)2 and ethoxytriemethyl silane (CH3)3Si (C2H5O). The result showed that permeability of original membranes for water (e.g., 1100 degrees C, 2.87 x 10(-3) mol/m2 s Pa) was larger than ethanol (1100 degrees C, 5.51 x 10(-4) mol/m2 s Pa) and toluene (1100 degrees C, 3.09 x 10(-4) mol/m2 s Pa) at the sintering temperatures. For the silane modified membranes, the permeability for water decreased drastically while those for ethanol and toluene increased.     

Synthesis of nanocrystalline Ce(0.8)Gd(0.2)O(2-delta) electrolyte materials for IT-SOFC

We successfully synthesized nano-sized Ce(0.8)Gd(0.2)O(2-delta) powders by combustion method, using gelatin as fuel. The calcined powders showed high-quality characteristics, i.e., nano-scale size (14-35 nm) and narrow size distribution. The structural, morphological, and electrical characteristics of the sintered Ce(0.8)Gd(0.2)O(2-delta) were studied systematically, depending on sintering temperature. The crystal structure of the Ce(0.8)Gd(0.2)O(2-delta) belonged to the cubic fluorite structure. The gelatin-assisted combustion synthesized Ce(0.8)Gd(0.2)O(2-delta) powders allowed to sinter well at low temperature for dense and ultra-fine Ce(0.8)Gd(0.2)O(2-delta) electrolyte with good electrical conductivity. The sintering temperature of the Ce(0.8)Gd(0.2)O2 powder was approximately 300 degrees C lower than that of conventional solid-state synthesized powder. The nanopowder produced was sintered into pellets with relative densities over 99.1% of the theoretical value even at 1400 degrees C. The Ce(0.8)Gd(0.2)O(2-delta) sintered at 1400 degrees C exhibited a conductivity of 0.101 S/cm at 800 degrees C in air.     

Grazing incidence X-ray scattering study of sol-gel derived indium tin oxide thin films

Indium tin oxide (ITO) thin film as one of promising transparent conducting oxide (TCO) films has attracted ever increasing attention owing to its special optical, photocatalytic and optoelectronic properties. In this research, ITO films were prepared by sol-gel dip-coating method and annealed at different temperatures subsequently. The lateral and surface structures of ITO films as well as the structural evolution have been assessed by grazing incidence small angle X-ray scattering (GISAXS) technique. The films show pore fractal structure when annealed at low temperature (≤ 800 °C) which transforms to a hierarchical fractal structure at high temperature (1000 °C). As the temperature rises, films are densified due to the elimination of small pores on the surface at low temperature and the shrinkage of big pores buried inside at high temperature. However, the surface roughness and porosity near the surface are improved at high annealing temperature.     

Effect of sintering temperature on the characteristics of sludge ceramsite

In order to investigate the effect of sintering temperature on the characteristics of sludge ceramsite and find an optimal sintering temperature, dried sewage sludge, clay, and water glass were mixed at ratios of dried sewage sludge/clay=33% and water glass/clay=15%. Then these mixtures were heated to 850, 900, 950, 1000, 1100, and 1200 degrees C for production of sludge ceramsite. The sludge ceramsite were characterized by DTA-TGA, SEM-EDS, XRD, and XRF. The results indicate that the differences in thermal behaviours are caused by the compositional and structural variations; the ceramsite sintered at 1000 degrees C has more uniformly distributed finer pores (0.5 microm相似文献   

Nondestructive monitoring of fabrication parameters of sintered iron powder compacts using ultrasonics

Ultrasonic characterization of sintered iron powder compacts made with different fabrication parameters (compaction pressure, sintering time and temperature) has been carried out. Longitudinal and shear velocities of samples up to a pore volume fraction of 0.216 were measured to study the effect of porosity. The measured values were compared with the values predicted by scattering and elasticity theories. This study shows that the longitudinal velocity of the sintered compacts may be used for monitoring the basic production parameters.     

Lithium metazirconate for nuclear application: physical and mechanical properties

Lithium metazirconate is a candidate in fusion reactor designs as a tritium-breeding material. An amorphous powder was synthesized by gelling zirconium propylate and lithium acetate: after heat treatment at 900 °C, pure Li₂ZrO₃-l was obtained. Preliminary tests made on sintered pellets, obtained from this powder, demonstrated an appropriate tritium release at low temperature, when the sample porosity was about 20% and the mean pore radius 3 μm. The subject of this paper was to realize a good compromise between mechanical properties and the spread porosity, necessary for tritium diffusion. Dilatometric investigations were performed on compacts of powders treated at 800, 900 and 1000 °C to identify the best temperature and time of sintering. The calcined powders were also uniaxially pressed at 200, 300 and 500 MPa: the green bodies were sintered at 1200, 1250 and 1300 °C for 2 or 4 h, in order to produce ceramics having different porosity. On the sintered bodies, the pore size distribution, the mean pore radius and mechanical properties were evaluated.     

On the filling of a pore in a solid-liquid nanodispersed system

Thermodynamic equations have been derived that describe the process of the liquid migration from a pore into the bulk of a sintered body. The existence of the migration pressure in a nanocomposite body has been proved and the condition for the equilibrium of a liquid in a pore has been deduced. A concept of a pore critical radius has been formulated and an expression for the radius value has been suggested. All pores, whose radii exceed the critical one, are stable in a sintered body. The pores, whose radii are below the critical radius, are filled by the liquid phase.     

Non-destructive evaluation of mechanical properties of poly (vinyl) alcohol-hydroxyapatite nanocomposites

Hydroxyapatite-poly (vinyl) alcohol nanocomposite powder was synthesized using varying poly (vinyl) alcohol concentrations. The dried powder was compacted into micro-porous disks at a load of 4 tons. The disks were sintered at 1200°C to evolve porous nanocomposites. Size and shape of the pores observed in the scanning electron micrographs were quantified by using image processing software. Ultrasound velocity measurements were done to evaluate mechanical properties non-destructively.     

Pore morphology and pore surface roughening in rocks: a small-angle neutron scattering investigation

Pore morphology and pore-matrix interface roughening in some metamorphosed sedimentary rocks, sandstones and igneous rocks have been investigated using small-angle neutron scattering (SANS), in the length scales of 20–1000 nm., which reveal the fractal nature of the rock-pore interfaces. Surface fractal dimension of the metamorphosed rocks and the sandstones has been estimated to be 2.8 while, that for the igneous rocks has been found to be 2.3. An attempt has been made to explain the relatively high surface fractal nature of the former rocks with the help of a computer simulation model based on the formation mechanisms of these rocks. SANS data indicate some ideas about the upper cut-off of the fractal geometry for the igneous rocks as well as for the sandstone, but no unambiguous cut-off value has been obtained for the metamorphosed rocks in the accessible length scale. The multiple scattering effect in these rock specimens has also been looked into by performing the SANS experiments for the two thicknesses on each specimen.     

粉末表面化学镀铜烧结不锈钢的组织和腐蚀行为

研究了不锈钢粉末表面化学镀铜对烧结不锈钢组织和耐蚀性的影响.实验表明,以化学包覆不锈钢粉的形式加入1～5wt%的铜,在1150℃液相烧结时,在烧结不锈钢中,铜元素分布的均匀性以及烧结体的密度比机械混合方式加入铜都有很大提高;同时通过电化学实验表明,化学镀铜方式有利于提高不锈钢烧结体的耐蚀性.     

Nanostructured hydroxyapatite by microwave sintering

In this work, nanostructured HA ceramics with dense microstructure were prepared by microwave sintering process and their microstructures were compared with the case of conventional sintering. Commercially obtained HA powder with Ca/P molar ratio of 1.67 was used as a starting material. The powder of granular type consists of nanocrystalline particles of 20-30 nm in size. The as-received HA powder or the powder calcined at 800 degrees C, followed by ball-milling was used for the preparation of HA disks. Microwave sintering was conducted at 1200 degrees C for 5 min with a heating rate of 50 degrees C/min. HA ceramics with the sintered densities of approximately 96-97% of the theoretical were obtained. XRD analysis showed that all detectable peaks are identical to pure hydroxyapatite. The HA sintered body made of calcined and ball-milled powder showed uniform microstructure with grain size of 300-400 nm and with finer sub-grains of 30-40 nm.     

Structure property relationships in porous sintered steels

The flat bending fatigue strength of a variety of carbon-free iron base sintered materials has been investigated varying density, sintering temperature and particularly the morphology of the base powder. All effects that lead to round pores improve the fatigue performance.The porosity of sintered iron and steel is characterised by a large majority of tiny spherical pores and a few big pores of high irregularity. It is this small fraction of large and irregular pores with their pronounced internal stress concentration which determines the fatigue strength of sintered porous materials, next to overall density and alloying effects.     

Spark-plasma-sintering of fine BaTiO3 powder prepared by a sol-crystal method

Spark-Plasma-Sintering (SPS) has been applied to fine BaTiO₃ powder (several nanometers) prepared by a sol-crystal method. The starting powder was densified to more than 95% of the theoretical X-ray density, and the obtained SPS pellets had an average grain size of less than 1 m, owning to the relatively low sintering temperature (900–1000°C) and short sintering period of ca. 3 min. The room temperature permittivity at 1 kHz for SPS samples sintered at 1000°C is ca. 10,000. This high room temperature permittivity value is attributed to electrical inhomogeneities within pellets; a resistive surface layer covers the inner pellet core that consists of oxygen-deficient BaTiO₃. The reduced pellet core is characteristic of SPS pellets formed from powders that contain small amounts of residual organic matter.     

以无机盐为原料制备钇稳定的氧化锆超滤膜

用无机盐ＺｒＯＣｌ_２·８Ｈ_２Ｏ和Ｙ（ＮＯ_３）_３·６Ｈ_２Ｏ为原料,以溶胶－凝胶技术路线,在多孔氧化铝支撑体上成功地制备了记稳定的氧化锆（ＹＳＺ）陶瓷膜．扫描电子显微镜（ＳＥＭ）分析表明,用沉淀、胶溶、成膜的溶胶－凝胶技术,不能制备表面无龟裂的ＹＳＺ膜．沉淀用共沸蒸馏法干燥,得到高分散性的ＹＳＺ粉体,再用超声法制备ＹＳＺ氧化物胶体,通过浸渍成膜,ＳＥＭ分析证明,ＹＳＺ膜表面无明显缺陷．室温氮气渗透实验进一步证明,膜结构完整．用等温氮吸附实验测定了无支撑体膜的孔径大小和分布,平均孔径约为６ｎｍ．用激光散射技术测定ＹＳＺ胶体粒子平均半径为１１６ｎｍ,透射电子显微镜观察表明,胶体粒子由大小约为２０ｎｍ的晶粒组成．     

Microstructure development in SnO2 with and without additives

The microstructure development in pure and ZnO-, Nb₂O₅- or (ZnO + Nb₂O₅)-containing SnO₂ has been studied. Sintering of pure SnO₂ proceeds by an evaporation-condensation mechanism and grain and pore sizes increase without densification. The pores are open with no closed pores developed. Grain and pore structures become homogeneous with sintering time. Sintered pure SnO₂ is porous and has large grains. Nb₂O₅ suppresses particle coarsening and pore growth but does not promote densification, leading to porous sintered bodies with small grains. ZnO and (ZnO + Nb₂O₅) promote densification but do not suppress particle and grain coarsening. The sintered body is composed of large grains with pores located on grain boundaries.     

Characterization of the Pore Structure of Ceramics via Propagation of Light and Infrared Radiation

The pore size distributions of alumina and magnesia ceramics were determined by measuring the directional-hemispherical transmittance and reflectance. These values are highly sensitive to changes of the pore structure. The partially sintered alumina samples were measured at room temperature in a wavelength range from 0.5 to 6 m. The equation of radiative transfer can be solved for absorbing and scattering media by a three-flux solution. With this three-flux solution the scattering coefficients were derived from the measured directional-hemispherical transmittance and reflectance. The scattering coefficients can also be calculated theoretically by the Mie theory, if the pore size distribution is known. Finally, the quantitative pore size distribution was determined by fitting the theoretical scattering coefficients to the experimental scattering coefficients. To check the correctness of the derived pore-size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures of the alumina samples were taken. The pore-size distribution was then derived by counting the pores and determining the diameters D of the spherical pores. Both results agree well and show that the new procedure is a valuable tool to extract structural information during the final sintering state.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.